Process for production of acrylic acid or its derivatives from hydroxypropionic acid or its derivatives

ABSTRACT

Processes for the catalytic dehydration of hydroxypropionic acid, hydroxypropionic acid derivatives, or mixtures thereof to acrylic acid, acrylic acid derivatives, or mixtures thereof with high yield and selectivity and without significant conversion to undesired side products, such as, acetaldehyde, propanoic acid, and acetic acid, are provided.

FIELD OF THE INVENTION

The present invention generally relates to processes that catalyticallyconvert hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof to acrylic acid, acrylic acid derivatives, or mixturesthereof. More specifically, the invention relates to processes usefulfor the dehydration of hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof to acrylic acid, acrylic acidderivatives, or mixtures thereof with high yield and selectivity toacrylic acid, acrylic acid derivatives, or mixtures thereof, shortresidence time, and without significant conversion of thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to undesired side products, such as, for example, acetaldehyde,propanoic acid, acetic acid, 2,3-pentanedione, carbon dioxide, andcarbon monoxide.

BACKGROUND OF THE INVENTION

Acrylic acid, acrylic acid derivatives, or mixtures thereof have avariety of industrial uses, typically consumed in the form of polymers.In turn, these polymers are commonly used in the manufacture of, amongother things, adhesives, binders, coatings, paints, polishes,detergents, flocculants, dispersants, thixotropic agents, sequestrants,and superabsorbent polymers, which are used in disposable absorbentarticles, including diapers and hygienic products, for example. Acrylicacid is commonly made from petroleum sources. For example, acrylic acidhas long been prepared by catalytic oxidation of propylene. These andother methods of making acrylic acid from petroleum sources aredescribed in the Kirk-Othmer Encyclopedia of Chemical Technology, Vol.1, pgs. 342-369 (5^(th) Ed., John Wiley & Sons, Inc., 2004).Petroleum-based acrylic acid contributes to greenhouse emissions due toits high petroleum derived carbon content. Furthermore, petroleum is anon-renewable material, as it takes hundreds of thousands of years toform naturally and only a short time to consume. As petrochemicalresources become increasingly scarce, more expensive, and subject toregulations for CO₂ emissions, there exists a growing need for bio-basedacrylic acid, acrylic acid derivatives, or mixtures thereof that canserve as an alternative to petroleum-based acrylic acid, acrylic acidderivatives, or mixtures thereof.

Many attempts have been made over the last 40 to 50 years to makebio-based acrylic acid, acrylic acid derivatives, or mixtures thereoffrom non-petroleum sources, such as lactic acid (also known as2-hydroxypropionic acid), 3-hydroxypropionic acid, glycerin, carbonmonoxide and ethylene oxide, carbon dioxide and ethylene, and crotonicacid. From these non-petroleum sources, only lactic acid is producedtoday in high yield from sugar (≧90% of theoretical yield, orequivalently, ≧0.9 g of lactic acid per g of sugar) and purity, andeconomics which could support producing acrylic acid cost competitivelyto petroleum-based acrylic acid. As such, lactic acid or lactatepresents a real opportunity of serving as feedstock for bio-basedacrylic acid, acrylic acid derivatives, or mixtures thereof. Also,3-hydroxypropionic acid is expected to be produced at commercial scalein a few years, and as such, 3-hydropropionic acid will present anotherreal opportunity of serving as feedstock for bio-based acrylic acid,acrylic acid derivatives, or mixtures thereof. Sulfate salts; phosphatesalts; mixtures of sulfate and phosphate salts; bases; zeolites ormodified zeolites; metal oxides or modified metal oxides; andsupercritical water are the main catalysts which have been used todehydrate lactic acid or lactate to acrylic acid, acrylic acidderivatives, or mixtures thereof in the past with varying success.

For example, in U.S. Pat. No. 4,786,756 (issued in 1988), the inventorsclaim the vapor phase dehydration of lactic acid or ammonium lactate toacrylic acid using aluminum phosphate (AlPO₄) treated with an aqueousinorganic base as a catalyst. As examples, the '756 patent discloses amaximum yield of acrylic acid of 43.3% when lactic acid was fed into thereactor at approximately atmospheric pressure, and a respective yield of61.1% when ammonium lactate was fed into the reactor. In both examples,acetaldehyde was produced at yields of 34.7% and 11.9%, respectively,and other side products were also present in large quantities, such as,propionic acid, CO, and CO₂. Omission of the base treatment causedincreased amounts of the side products. Another example is Hong et al.(2011) Appl. Catal. A: General 396:194-200, who developed and testedcomposite catalysts made with Ca₃(PO₄)₂ and Ca₂(P₂O₇) salts with aslurry-mixing method. The catalyst with the highest yield of acrylicacid from methyl lactate was the 50%-50% (by weight) catalyst. Ityielded 68% acrylic acid, about 5% methyl acrylate, and about 14%acetaldehyde at 390° C. The same catalyst achieved 54% yield of acrylicacid, 14% yield of acetaldehyde, and 14% yield of propionic acid fromlactic acid.

Prof. D. Miller's group at Michigan State University (MSU) publishedmany papers on the dehydration of lactic acid or lactic acid esters toacrylic acid and 2,3-pentanedione, such as, Gunter et al. (1994) J.Catalysis 148:252-260; and Tam et al. (1999) Ind. Eng. Chem. Res.38:3873-3877. The best acrylic acid yields reported by the group wereabout 33% when lactic acid was dehydrated at 350° C. over low surfacearea and pore volume silica impregnated with NaOH. In the sameexperiment, the acetaldehyde yield was 14.7% and the propionic acidyield was 4.1%. Examples of other catalysts tested by the group wereNa₂SO₄, NaCl, Na₃PO₄, NaNO₃, Na₂SiO₃, Na₄P₂O₇, NaH₂PO₄, Na₂HPO₄,Na₂HAsO₄, NaC₃H₅O₃, NaOH, CsCl, Cs₂SO₄, KOH, CsOH, and LiOH. In allcases, the above referenced catalysts were tested as individualcomponents, not in mixtures. Finally, the group suggested that the yieldto acrylic acid is improved and the yield to the side products issuppressed when the surface area of the silica support is low, reactiontemperature is high, reaction pressure is low, and residence time of thereactants in the catalyst bed is short.

Finally, the Chinese patent application 200910054519.7 discloses the useof ZSM-5 molecular sieves modified with aqueous alkali (such as, NH₃,NaOH, and Na₂CO₃) or a phosphoric acid salt (such as, NaH₂PO₄, Na₂HPO₄,LiH₂PO₄, LaPO₄, etc.). The best yield of acrylic acid achieved in thedehydration of lactic acid was 83.9%, however that yield came at verylong residence times.

Therefore, the manufacture of acrylic acid, acrylic acid derivatives, ormixtures thereof from lactic acid or lactate by processes, such as thosedescribed in the literature noted above, leads to: 1) yields of acrylicacid, acrylic acid derivatives, or mixtures thereof not exceeding 70%;2) low selectivities of acrylic acid, acrylic acid derivatives, ormixtures thereof, i.e., significant amounts of undesired side products,such as, acetaldehyde, 2,3-pentanedione, propionic acid, CO, and CO₂; 3)long residence times in the catalyst beds; and 4) catalyst deactivationin short time on stream (TOS). The side products can deposit onto thecatalyst resulting in fouling, and premature and rapid deactivation ofthe catalyst. Further, once deposited, these side products can catalyzeother undesired reactions, such as polymerization reactions. Aside fromdepositing on the catalysts, these side products, even when present inonly small amounts, impose additional costs in processing acrylic acid(when present in the reaction product effluent) in the manufacture ofsuperabsorbent polymers (SAP), for example. These deficiencies of theprior art processes and catalysts render them commercially non-viable.

Accordingly, there is a need for processes for the dehydration ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereof,with high yield, selectivity, and efficiency (i.e., short residencetime), and high longevity catalysts.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a process for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided comprising the following steps:

-   -   a) Providing an aqueous solution comprising hydroxypropionic        acid, hydroxypropionic acid derivatives, or mixtures thereof,        wherein said hydroxypropionic acid is in monomeric form in said        aqueous solution;    -   b) Combining said aqueous solution with an inert gas to form an        aqueous solution/gas blend;    -   c) Evaporating said aqueous solution/gas blend to produce a        gaseous mixture; and    -   d) Dehydrating said gaseous mixture by contacting said gaseous        mixture with a dehydration catalyst under a pressure of at least        about 80 psig, producing said acrylic acid, acrylic acid        derivatives, or mixtures thereof.

In another embodiment of the present invention, a process for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided comprising the following steps:

-   -   a) Providing an aqueous solution comprising hydroxypropionic        acid, hydroxypropionic acid derivatives, or mixtures thereof,        wherein said hydroxypropionic acid comprises oligomers in said        aqueous solution;    -   b) Heating said aqueous solution at a temperature from about        50° C. to about 100° C. to remove said oligomers of said        hydroxypropionic acid and produce an aqueous solution of        monomeric hydroxypropionic acid;    -   c) Combining said aqueous solution of monomeric hydroxypropionic        acid with an inert gas to form an aqueous solution/gas blend;    -   d) Evaporating said aqueous solution/gas blend to produce a        gaseous mixture; and    -   e) Dehydrating said gaseous mixture by contacting said mixture        with a dehydration catalyst, producing said acrylic acid,        acrylic acid derivatives and mixtures thereof.

In yet another embodiment of the present invention, a process forconverting hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof to acrylic acid, acrylic acid derivatives, or mixturesthereof is provided comprising the following steps:

-   -   a) Providing an aqueous solution comprising hydroxypropionic        acid, hydroxypropionic acid derivatives, or mixtures thereof,        wherein said hydroxypropionic acid is in monomeric form in said        aqueous solution;    -   b) Combining said aqueous solution with an inert gas to form an        aqueous solution/gas blend;    -   c) Evaporating said aqueous solution/gas blend to produce a        gaseous mixture;    -   d) Dehydrating said gaseous mixture by contacting said mixture        with a dehydration catalyst, producing said acrylic acid,        acrylic acid derivatives, or mixtures thereof; and    -   e) Cooling said acrylic acid, acrylic acid derivatives, or        mixtures thereof at a GHSV of more than about 360 h⁻¹.

In one embodiment of the present invention, a process for convertinglactic acid to acrylic acid is provided comprising the following steps:

-   -   a) Diluting an about 88% lactic acid aqueous solution with water        to form an about 20 wt % lactic acid aqueous solution;    -   b) Heating said about 20 wt % lactic acid aqueous solution at a        temperature from about 95° C. to about 100° C. to remove        oligomers of said lactic acid, producing a monomeric lactic acid        aqueous solution comprising at least 95 wt % of said lactic acid        in monomeric form based on the total amount of lactic acid;    -   c) Combining said monomeric lactic acid aqueous solution with        nitrogen to form an aqueous solution/gas blend;    -   d) Evaporating said aqueous solution/gas blend in a reactor with        inside surface of borosilicate glass at a GHSV of about 7,200        h⁻¹ at a temperature from about 300° C. to about 350° C. to        produce a gaseous mixture comprising about 2.5 mol % lactic acid        and about 50 mol % water;    -   e) Dehydrating said gaseous mixture in a reactor with inside        surface of borosilicate glass at a GHSV of about 3,600 h⁻¹ at a        temperature from about 350° C. to about 425° C. by contacting        said mixture with a dehydration catalyst under a pressure of        about 360 psig, producing said acrylic acid; and    -   f) Cooling said acrylic acid to give an acrylic acid solution at        a GHSV from about 360 h⁻¹ to about 36,000 h⁻¹.

In another embodiment of the present invention, a process for convertinghydroxypropionic acid, derivatives of hydroxypropionic acid, andmixtures thereof to acrylic acid, acrylic acid derivatives, or mixturesthereof is provided comprising the following steps:

-   -   a) Providing an aqueous solution comprising hydroxypropionic        acid, hydroxypropionic acid derivatives, or mixtures thereof,        wherein said hydroxypropionic acid is in monomeric form in said        aqueous solution, and wherein the hydroxypropionic acid,        hydroxypropionic acid derivatives, or mixtures thereof comprise        from about 10 wt % to about 25 wt % of said aqueous solution;    -   b) Combining said aqueous solution with an inert gas to form an        aqueous solution/gas blend;    -   c) Evaporating said aqueous solution/gas blend to produce a        gaseous mixture; and    -   d) Dehydrating said gaseous mixture by contacting said mixture        with a dehydration catalyst producing said acrylic acid, acrylic        acid derivatives, or mixtures thereof.

In yet another embodiment of the present invention, a process forconverting alkyl lactates to acrylic acid, acrylic acid derivatives, ormixtures thereof is provided comprising the following steps:

-   -   a) Providing alkyl lactates or a solution comprising alkyl        lactates and a solvent;    -   b) Combining said alkyl lactates or said solution comprising        said alkyl lactates and said solvent with an inert gas to form a        liquid/gas blend;    -   c) Evaporating said liquid/gas blend to produce a gaseous        mixture; and    -   d) Dehydrating said gaseous mixture by contacting said gaseous        mixture with a dehydration catalyst under a pressure of at least        about 80 psig, producing said acrylic acid, acrylic acid        derivatives, or mixtures thereof.

Additional features of the invention may become apparent to thoseskilled in the art from a review of the following detailed description,taken in conjunction with the examples and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

I Definitions

As used herein, the term “condensed phosphate” refers to any saltscontaining one or several P-O-P bonds generated by corner sharing of PO₄tetrahedra.

As used herein, the term “cyclophosphate” refers to any cyclic condensedphosphate constituted of two or more corner-sharing PO₄ tetrahedra.

As used herein, the term “monophosphate” or “orthophosphate” refers toany salt whose anionic entity, [PO₄]³⁻, is composed of four oxygen atomsarranged in an almost regular tetrahedral array about a centralphosphorus atom.

As used herein, the term “oligophosphate” refers to any polyphosphatesthat contain five or less PO₄ units.

As used herein, the term “polyphosphate” refers to any condensedphosphates containing linear P-O-P linkages by corner sharing of PO₄tetrahedra leading to the formation of finite chains.

As used herein, the term “ultraphosphate” refers to any condensedphosphate where at least two PO₄ tetrahedra of the anionic entity sharethree of their corners with the adjacent ones.

As used herein, the term “cation” refers to any atom or group ofcovalently-bonded atoms having a positive charge.

As used herein, the term “monovalent cation” refers to any cation with apositive charge of +1.

As used herein, the term “polyvalent cation” refers to any cation with apositive charge equal or greater than +2.

As used herein, the term “anion” refers to any atom or group ofcovalently-bonded atoms having a negative charge.

As used herein, the term “heteropolyanion” refers to any anion withcovalently bonded XO_(p) and YO_(r) polyhedra, and thus includes X—O—Yand possibly X—O—X and Y—O—Y bonds, wherein X and Y represent any atoms,and wherein p and r are any positive integers.

As used herein, the term “heteropolyphosphate” refers to anyheteropolyanion, wherein X represents phosphorus (P) and Y representsany other atom.

As used herein, the term “phosphate adduct” refers to any compound withone or more phosphate anions and one or more non-phosphate anions thatare not covalently linked.

As used herein, the terms “LA” refers to lactic acid, “AA” refers toacrylic acid, “AcH” refers to acetaldehyde, and “PA” refers to propionicacid.

As used herein, the term “particle span” refers to a statisticalrepresentation of a given particle sample and is equal to(D_(v,0.90)−D_(v,0.10))/D_(v,0.50). The term “median particle size” orD_(v,0.50) refers to the diameter of a particle below which 50% of thetotal volume of particles lies. Further, D_(v,0.10) refers to theparticle size that separates the particle sample at the 10% by volumefraction and D_(v,0.90), is the particle size that separates theparticle sample at the 90% by volume fraction.

As used herein, the term “conversion” in % is defined as[hydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof flow rate in (mol/min)−hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof flow rate out(mol/min)]/[hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof flow rate in (mol/min)]*100. For the purposes of thisinvention, the term “conversion” means molar conversion, unlessotherwise noted.

As used herein, the term “yield” in % is defined as [product flow rateout (mol/min)/hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof flow rate in (mol/min)]*100. For the purposes ofthis invention, the term “yield” means molar yield, unless otherwisenoted.

As used herein, the term “selectivity” in % is defined as[Yield/Conversion]*100. For the purposes of this invention, the term“selectivity” means molar selectivity, unless otherwise noted.

As used herein, the term “total flow rate out” in mol/min and forhydroxypropionic acid is defined as: (2/3)*[C2 flow rate out(mol/min)]+[C3 flow rate out (mol/min)]+(2/3)*[acetaldehyde flow rateout (mol/min)]+(4/3)*[C4 flow rate out (mol/min)]+[hydroxypropionic acidflow rate out (mol/min)]+[pyruvic acid flow rate out(mol/min)]+(2/3)*[acetic acid flow rate out (mol/min)]+[1,2-propanediolflow rate out (mol/min)]+[propionic acid flow rate out(mol/min)]+[acrylic acid flow rate out(mol/min)]+(5/3)*[2,3-pentanedione flow rate out (mol/min)]+(⅓)*[carbonmonoxide flow rate out (mol/min)]+(1/3)*[carbon dioxide flow rate out(mol/min)]. If a hydroxypropionic acid derivative is used instead ofhydroxypropionic acid, the above formula needs to be adjusted accordingto the number of carbon atoms in the hydroxypropionic acid derivative.

As used herein, the term “C2” means ethane and ethylene.

As used herein, the term “C3” means propane and propylene.

As used herein, the term “C4” means butane and butenes.

As used herein, the term “total molar balance” or “TMB” in % is definedas [total flow rate out (mol/min)/hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof flow rate in(mol/min)]*100.

As used herein, the term “the acrylic acid yield was corrected for TMB”is defined as [acrylic acid yield/total molar balance]*100, to accountfor slightly higher flows in the reactor.

As used herein, the term “Gas Hourly Space Velocity” or “GHSV” in h⁻¹ isdefined as [Total gas flow rate (mL/min)/catalyst bed volume (mL)]/60.The total gas flow rate is calculated under Standard Temperature andPressure conditions (STP; 0° C. and 1 atm).

As used herein, the term “Liquid Hourly Space Velocity” or “LHSV” in h⁻¹is defined as [Total liquid flow rate (mL/min)/catalyst bed volume(mL)]/60.

II Process

The inventors have unexpectedly found that the process of dehydratinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof can produce high yield to and selectivity of acrylic acid,acrylic acid derivatives, or mixtures thereof when the solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof has the hydroxypropionic acid in monomeric form and it iscombined with an inert gas, and the process includes an evaporation stepand a dehydration step. Furthermore, a cooling step with a shortresidence time, downstream of the dehydration step, and operating thedehydration step under a pressure of 80 psig or more aid in theachievement of the high yield and selectivity of acrylic acid, acrylicacid derivatives, or mixtures thereof.

A process for converting hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof to acrylic acid, acrylic acidderivatives, or mixtures thereof of the present invention comprises thefollowing steps: a) providing an aqueous solution comprisinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof, wherein said hydroxypropionic acid is in monomeric form in theaqueous solution; b) combining the aqueous solution with an inert gas toform an aqueous solution/gas blend; c) evaporating the aqueous solutiongas/blend to produce a gaseous mixture; and d) dehydrating the gaseousmixture by contacting the mixture with a dehydration catalyst under apressure of at least about 80 psig.

Hydroxypropionic acid can be 3-hydroxypropionic acid, 2-hydroxypropionicacid (also called, lactic acid), 2-methyl hydroxypropionic acid, ormixtures thereof. Derivatives of hydroxypropionic acid can be metal orammonium salts of hydroxypropionic acid, alkyl esters ofhydroxypropionic acid, alkyl esters of 2-methyl hydroxypropionic acid,cyclic di-esters of hydroxypropionic acid, hydroxypropionic acidanhydride, or a mixture thereof. Non-limiting examples of metal salts ofhydroxypropionic acid are sodium hydroxypropionate, potassiumhydroxypropionate, and calcium hydroxypropionate. Non-limiting examplesof alkyl esters of hydroxypropionic acid are methyl hydroxypropionate,ethyl hydroxypropionate, butyl hydroxypropionate, 2-ethylhexylhydroxypropionate, or mixtures thereof. A non-limiting example of cyclicdi-esters of hydroxypropionic acid is dilactide.

Hydroxypropionic acid can be in monomeric form or as oligomers in anaqueous solution of hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof. In one embodiment, the oligomers ofthe hydroxypropionic acid in an aqueous solution of hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof are lessthan about 25 wt % based on the total amount of hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof. In anotherembodiment, the oligomers of the hydroxypropionic acid in an aqueoussolution of hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof are less than about 10 wt % based on the total amountof hydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof. In another embodiment, the oligomers of the hydroxypropionicacid in an aqueous solution of hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof are less than about 5 wt % basedon the total amount of hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof. In yet another embodiment, thehydroxypropionic acid is in monomeric form in an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof. The process steps to remove the oligomers from the aqueoussolution can be purification or diluting with water and heating. In oneembodiment, the heating step can involve heating the aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof at a temperature from about 50° C. to about 100° C. to removethe oligomers of the hydroxypropionic acid. In another embodiment, theheating step can involve heating the lactic acid aqueous solution at atemperature from about 95° C. to about 100° C. to remove the oligomersof the lactic acid and produce a monomeric lactic acid aqueous solutioncomprising at least 95 wt % of lactic acid in monomeric form based onthe total amount of lactic acid. In another embodiment, an about 88 wt %lactic acid aqueous solution (e.g. from Purac Corp., Lincolnshire, Ill.)is diluted with water to form an about 20 wt % lactic acid aqueoussolution, to remove the ester impurities that are produced from theintermolecular condensation reaction. These esters can result in loss ofproduct due to their high boiling point and oligomerization in theevaporation stage of the process. Additionally, these esters can causecoking, catalyst deactivation, and reactor plugging. As the watercontent decreases in the aqueous solution, the loss of feed material tothe catalytic reaction, due to losses in the evaporation step,increases.

In one embodiment, the hydroxypropionic acid is lactic acid or 2-methyllactic acid. In another embodiment, the hydroxypropionic acid is lacticacid. Lactic acid can be L-lactic acid, D-lactic acid, or mixturesthereof. In one embodiment, the hydroxypropionic acid derivative ismethyl lactate. Methyl lactate can be neat or in an aqueous solution.

Acrylic acid derivatives can be metal or ammonium salts of acrylic acid,alkyl esters of acrylic acid, acrylic acid oligomers, or a mixturethereof. Non-limiting examples of metal salts of acrylic acid are sodiumacrylate, potassium acrylate, and calcium acrylate. Non-limitingexamples of alkyl esters of acrylic acid are methyl acrylate, ethylacrylate, butyl acrylate, 2-ethylhexyl acrylate, or mixtures thereof.

In one embodiment, the concentration of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof in the aqueoussolution is between about 5 wt % and about 50 wt %. In anotherembodiment, the concentration of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof in the aqueoussolution is between about 10 wt % and about 25 wt %. In yet anotherembodiment, the concentration of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof in the aqueoussolution is about 20 wt %.

The aqueous solution can be combined with an inert gas to form anaqueous solution/gas blend. Non-limiting examples of the inert gas areair, nitrogen, helium, argon, carbon dioxide, carbon monoxide, steam,and mixtures thereof. The inert gas can be introduced to the evaporatingstep separately or in combination with the aqueous solution. The aqueoussolution can be introduced with a simple tube or through atomizationnozzles. Non-limiting examples of atomization nozzles include fannozzles, pressure swirl atomizers, air blast atomizers, two-fluidatomizers, rotary atomizers, and supercritical carbon dioxide atomizers.In one embodiment, the droplets of the aqueous solution are less thanabout 500 μm in diameter. In another embodiment, the droplets of theaqueous solution are less than about 200 μm in diameter. In yet anotherembodiment, the droplets of the aqueous solution are less than about 100μm in diameter.

In the evaporating step, the aqueous solution/gas blend is heated togive a gaseous mixture. In one embodiment, the temperature during theevaporating step is from about 165° C. to about 450° C. In anotherembodiment, the temperature during the evaporating step is from about250° C. to about 375° C. In one embodiment, the gas hourly spacevelocity (GHSV) in the evaporating step is from about 720 ⁻¹ to 3,600h⁻¹. In another embodiment, the gas hourly space velocity (GHSV) in theevaporating step is about 7,200 h⁻¹. The evaporating step can beperformed at either atmospheric pressure or higher pressure. In oneembodiment, the evaporating step is performed under a pressure fromabout 80 psig to about 550 psig. In another embodiment, the evaporatingstep is performed under a pressure from about 300 psig to about 400psig. In yet another embodiment, the evaporating step is performed undera pressure from about 350 psig to about 375 psig. In one embodiment, thegaseous mixture comprises from about 0.5 mol % to about 50 mol %hydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof. In another embodiment, the gaseous mixture comprises from about1 mol % to about 10 mol % hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof. In another embodiment, the gaseousmixture comprises from about 1.5 mol % to about 3.5 mol %hydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof. In another embodiment, the gaseous mixture comprises about 2.5mol % hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof.

The evaporating step can be performed in various types of equipment,such as, but not limited to, plate heat exchanger, empty flow reactor,and fixed bed flow reactor. Regardless of the type of the reactor, inone embodiment, the reactor has an interior surface comprising materialselected from the group consisting of quartz, borosilicate glass,silicon, hastelloy, inconel, manufactured sapphire, stainless steel, andmixtures thereof. In another embodiment, the reactor has an interiorsurface comprising material selected from the group consisting ofquartz, borosilicate glass, and mixtures thereof. The evaporating stepcan be performed in a reactor with the aqueous solution flowing down, orflowing up, or flowing horizontally. In one embodiment, the evaporatingstep is performed in a reactor with the aqueous solution flowing down.Also, the evaporating step can be done in a batch form.

The gaseous mixture from the evaporating step is converted to acrylicacid, acrylic acid derivatives, and mixture thereof by contact it with adehydration catalyst in the dehydrating step. The dehydration catalystcan be selected from the group comprising sulfates, phosphates, metaloxides, aluminates, silicates, aluminosilicates (e.g., zeolites),arsenates, nitrates, vanadates, niobates, tantalates, selenates,arsenatophosphates, phosphoaluminates, phosphoborates, phosphocromates,phosphomolybdates, phosphosilicates, phosphosulfates, phosphotungstates,and mixtures thereof, and others that may be apparent to those havingordinary skill in the art. The catalyst can contain an inert supportthat is constructed of a material comprising silicates, aluminates,carbons, metal oxides, and mixtures thereof. In one embodiment, thedehydrating step is performed in a reactor, wherein the reactor has aninterior surface comprising material selected from the group consistingof quartz, borosilicate glass, silicon, hastelloy, inconel, manufacturedsapphire, stainless steel, and mixtures thereof. In another embodiment,the dehydrating step is performed in a reactor, wherein the reactor hasan interior surface comprising material selected from the groupconsisting of quartz, borosilicate glass, and mixtures thereof. In oneembodiment, the temperature during the dehydrating step is from about150° C. to about 500° C. In another embodiment, the temperature duringthe dehydrating step is from about 300° C. to about 450° C. In oneembodiment, the GHSV in the dehydrating step is from about 720 h⁻¹ toabout 36,000 h⁻¹. In another embodiment, the GHSV in the dehydratingstep is about 3,600 h⁻¹. The dehydrating step can be performed at higherthan atmospheric pressure. In one embodiment, the dehydrating step isperformed under a pressure of at least about 80 psig. In anotherembodiment, the dehydrating step is performed under a pressure fromabout 80 psig to about 550 psig. In another embodiment, the dehydratingstep is performed under a pressure from about 150 psig to about 500psig. In yet another embodiment, the dehydrating step is performed undera pressure from about 300 psig to about 400 psig. The dehydrating stepcan be performed in a reactor with the gaseous mixture flowing down,flowing up, or flowing horizontally. In one embodiment, the dehydratingstep is performed in a reactor with the gaseous mixture flowing down.Also, the dehydrating step can be done in a batch form.

In one embodiment, the evaporating and dehydrating steps are combined ina single step. In another embodiment, the evaporating and dehydratingsteps are performed sequentially in a single reactor. In yet anotherembodiment, the evaporating and dehydrating steps are performedsequentially in a tandem reactor.

In one embodiment, the selectivity of acrylic acid, acrylic acidderivatives, and mixture thereof from hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof is at least about50%. In another embodiment, the selectivity of acrylic acid, acrylicacid derivatives, and mixture thereof from hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof is at least about80%. In one embodiment, the selectivity of propanoic acid fromhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof is less than about 5%. In another embodiment, the selectivity ofpropanoic acid from hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof is less than about 1%. In oneembodiment, the conversion of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof is more thanabout 50%. In another embodiment, the conversion of the hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof is morethan about 80%.

In another embodiment of the present invention, a process for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofis provided. The process comprises the following steps: a) providing anaqueous solution comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof, wherein the hydroxypropionic acidcomprises oligomers in the aqueous solution; b) heating the aqueoussolution at a temperature from about 50° C. to about 100° C. to removethe oligomers of the hydroxypropionic acid and produce an aqueoussolution of monomeric hydroxypropionic acid; c) combining the aqueoussolution of monomeric hydroxypropionic acid with an inert gas to form anaqueous solution/gas blend; d) evaporating the aqueous solutiongas/blend to produce a gaseous mixture; and e) dehydrating the gaseousmixture by contacting the mixture with a dehydration catalyst andproducing the acrylic acid, acrylic acid derivatives, or mixturesthereof.

In one embodiment, after the heating step, the concentration of theoligomers of the hydroxypropionic acid in the aqueous solution ofmonomeric of monomeric hydroxypropionic acid is less than about 20 wt %based on the total amount of hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof. In another embodiment, after theheating step, the concentration of the oligomers of the hydroxypropionicacid in the aqueous solution of monomeric of monomeric hydroxypropionicacid is less than about 5 wt % based on the total amount ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof.

In another embodiment of the present invention, a process for convertinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, and mixture thereofis provided. The process comprises the following steps: a) providing anaqueous solution comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof, wherein the hydroxypropionic acid isin monomeric form in the aqueous solution; b) combining the aqueoussolution with an inert gas to form an aqueous solution/gas blend; c)evaporating the aqueous solution/gas blend to produce a gaseous mixture;d) dehydrating the gaseous mixture by contacting the mixture with adehydration catalyst producing acrylic acid, and/or acrylates; and e)cooling the acrylic acid, acrylic acid derivatives, and mixture thereofat a GHSV of more than about 360 h⁻¹.

The stream of acrylic acid, acrylic acid derivatives, and mixturethereof produced in the dehydrating step is cooled to give an aqueousacrylic acid composition as the product stream. The time required tocool stream of the acrylic acid, acrylic acid derivatives, or mixturesthereof must be controlled to reduce the decomposition of acrylic acidto ethylene and polymerization. In one embodiment, the GHSV of theacrylic acid, acrylic acid derivatives, and mixture thereof in thecooling step is more than about 720 h⁻¹.

In another embodiment of the present invention, a process for convertinglactic acid to acrylic acid is provided. The process comprises thefollowing steps: a) diluting an about 88 wt % lactic acid aqueoussolution with water to form an about 20 wt % lactic acid aqueoussolution; b) heating the about 20 wt % lactic acid aqueous solution at atemperature of about 95° C. to about 100° C. to remove oligomers of thelactic acid, producing a monomeric lactic acid solution comprising atleast about 95 wt % of the lactic acid in monomeric form based on thetotal amount of lactic acid; c) combining the monomeric lactic acidsolution with nitrogen to form an aqueous solution/gas blend; d)evaporating the aqueous solution/gas blend in a reactor with insidesurface of borosilicate glass at a GHSV of about 7,200 h⁻¹ at atemperature from about 300° C. to about 350° C. to produce a gaseousmixture comprising about 2.5 mol % lactic acid and about 50 mol % water;e) dehydrating the gaseous mixture in a reactor with inside surface ofborosilicate glass at a GHSV of about 3,600 h⁻¹ at a temperature of 350°C. to about 425° C. by contacting the mixture with a dehydrationcatalyst under a pressure of about 360 psig, producing the acrylic acid;and f) cooling the acrylic acid at a GHSV from about 360 h⁻¹ to about36,000 h⁻¹.

In another embodiment of the present invention, a process for convertinghydroxypropionic acid, derivatives of hydroxypropionic acid, andmixtures thereof to acrylic acid, acrylic acid derivatives, or mixturesthereof is provided. The process comprises the following steps: a)providing an aqueous solution comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof, wherein thehydroxypropionic acid is in monomeric form in the aqueous solution, andwherein the hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof comprise from about 10 wt % to about 25 wt % of theaqueous solution; b) combining the aqueous solution with an inert gas toform an aqueous solution/gas blend; c) evaporating the aqueoussolution/gas blend to produce a gaseous mixture; and d) dehydrating thegaseous mixture by contacting the mixture with a dehydration catalystproducing acrylic acid, acrylic acid derivatives, or mixtures thereof.

In another embodiment of the present invention, a process for convertingalkyl lactates to acrylic acid, acrylic acid derivatives, or mixturesthereof is provided. The process comprises the following steps: a)providing alkyl lactates or a solution comprising alkyl lactates and asolvent; b) combining said alkyl lactates or said solution comprisingsaid alkyl lactates and said solvent with an inert gas to form aliquid/gas blend; c) evaporating said liquid/gas blend to produce agaseous mixture; and d) dehydrating said gaseous mixture by contactingsaid gaseous mixture with a dehydration catalyst under a pressure of atleast about 80 psig, producing acrylic acid, acrylic acid derivatives,or mixtures thereof.

In one embodiment, alkyl lactates are selected from the group consistingof methyl lactate, ethyl lactate, butyl lactate, 2-ethylhexyl lactate,and mixtures thereof. In another embodiment, the solvent is selectedfrom the group consisting of water, methanol, ethanol, butanol,2-ethylhexanol, isobutanol, isooctyl alcohol, and mixtures thereof.

III Catalysts for the Conversion of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives

In one embodiment, the catalyst comprises: (a) at least one condensedphosphate anion selected from the group consisting of formulae (I),(II), and (III),[P_(n)O_(3n+1)]^((n+2)−)  (I)[P_(n)O_(3n)]^(n−)  (II)[P_((2m+n))O_((5m+3n))]^(n−)  (III)wherein n is at least 2 and m is at least 1, and (b) at least twodifferent cations, wherein the catalyst is essentially neutrallycharged, and further, wherein the molar ratio of phosphorus to the atleast two different cations is between about 0.7 and about 1.7.

The anions defined by formulae (I), (II), and (III) are also referred toas polyphosphates (or oligophosphates), cyclophosphates, andultraphosphates, respectively.

In another embodiment, the catalyst comprises: (a) at least onecondensed phosphate anion selected from the group consisting of formulae(I) and (II)[P_(n)O_(3n+1)]^((n+2)−)  (I)[P_(n)O_(3n)]^(n−)  (II)wherein n is at least 2, and (b) at least two different cations, whereinthe catalyst is essentially neutrally charged, and further, wherein themolar ratio of phosphorus to the at least two different cations isbetween about 0.7 and about 1.7.

The cations can be monovalent or polyvalent. In one embodiment, onecation is monovalent and the other cation is polyvalent. In anotherembodiment, the polyvalent cation is selected from the group consistingof divalent cations, trivalent cations, tetravalent cations, pentavalentcations, and mixtures thereof. Non-limiting examples of monovalentcations are H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag+, Rb⁺, T1 ⁺, and mixturesthereof. In one embodiment, the monovalent cation is selected from thegroup consisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and mixtures thereof; inanother embodiment, the monovalent cation is Na⁺or K⁺; and in yetanother embodiment, the monovalent cation is K⁺. Non-limiting examplesof polyvalent cations are cations of the alkaline earth metals (i.e.,Be, Mg, Ca, Sr, Ba, and Ra), transition metals (e.g. Y, Ti, Zr, V, Nb,Cr, Mo, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Cu, Ag, and Au), poor metals(e.g. Zn, Ga, Si, Ge, B, Al, In, Sb, Sn, Bi, and Pb), lanthanides (e.g.La and Ce), and actinides (e.g. Ac and Th). In one embodiment, thepolyvalent cation is selected from the group consisting of Be²⁺, Mg²⁺,Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Sn²⁺, Pb²⁺,Ti³⁺, Cr³⁺, Mn³⁺, Fe³⁺, Al³⁺, Ga³⁺, Y³⁺, In³⁺, Sb³⁺, Bi³⁺, Si⁴⁺, Ti⁴⁺,V⁴⁺, Ge⁴⁺, Mo⁴⁺, Pt⁴⁺, V⁵⁺, Nb⁵⁺, Sb⁵⁺, and mixtures thereof. In oneembodiment, the polyvalent cation is selected from the group consistingof Ca²⁺, Ba²⁺, Cu²⁺, Mn²⁺, Mn³⁺, and mixtures thereof; in anotherembodiment, the polyvalent cation is selected from the group consistingof Ca²⁺, Ba²⁺, Mn³⁺, and mixtures thereof; and in yet anotherembodiment, the polyvalent cation is Ba²⁺.

The catalyst can include cations: (a) H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, ormixtures thereof; and (b) Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Fe²⁺,Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Sn²⁺, Pb²⁺, Ti³⁺, Cr³⁺, Mn³⁺, Fe³⁺, Al³⁺,Ga³⁺, Y³⁺, In³⁺, Sb³⁺, Bi³⁺, Si⁴⁺, Ti⁴⁺, V⁴⁺, Ge⁴⁺, Mo⁴⁺, Pt⁴⁺, V⁵⁺,Nb⁵⁺, Sb⁵⁺, or mixtures thereof. In one embodiment the catalystcomprises Li⁺, Na^(+ , or K) ⁺ as monovalent cation, and Ca²⁺, Ba²⁺, orMn³⁺ as polyvalent cation; in another embodiment, the catalyst comprisesNa⁺ or K⁺ as monovalent cation, and Ca²⁺ or Ba²⁺ as polyvalent cation;and in yet another embodiment, the catalyst comprises K^(±)as themonovalent cation and Ba²⁺ as the polyvalent cation.

In one embodiment, the catalyst comprises Ba_(2−x−s)K_(2x)H_(2s)P₂O₇ and(KPO₃)_(n), wherein x and s are greater or equal to 0 and less thanabout 0.5 and n is a positive integer. In another embodiment, thecatalyst comprises Ca_(2−x−s)K_(2x)H_(2s)P₂O₇ and (KPO₃)_(n), wherein xand s are greater or equal to 0 and less than about 0.5 and n is apositive integer. In yet another embodiment, the catalyst comprisesMn_(1−x−s)K_(1+3x)H_(3s)P₂O₇ or Mn_(1−x−s)K_(2+2x)H_(2s)P₂O₇ and(KPO₃)_(n) wherein x and s are greater or equal to 0 and less than about0.5 and n is a positive integer. In another embodiment, the catalystcomprises any blend of Ba_(2−x−s)K_(2x)H_(2s)P₂O₇,Ca_(2−x−s)K_(2x)H_(2s)P₂O₇, Mn_(1−x−s)K_(1+3x)H_(3s)P₂O₇ orMn_(1−x−s)K_(2+2x)H_(2s)P₂O₇; (KPO₃)_(n), wherein x and s are greater orequal to 0 and less than about 0.5 and n is a positive integer.

In one embodiment, the molar ratio of phosphorus to the cations in thecatalyst is between about 0.7 and about 1.7; in another embodiment, themolar ratio of phosphorus to the cations in the catalyst is betweenabout 0.8 and about 1.3; and in yet another embodiment, the molar ratioof phosphorus to the cations in the catalyst is about 1.

In one embodiment, the catalyst comprises: (a) at least two differentcondensed phosphate anions selected from the group consisting offormulae (I), (II), and (III),[P_(n)O_(3n+1)]^((n+2)−)  (I)[P_(n)O_(3n)]^(n−)  (II)[P_((2m+n))O_((5m+3n))]^(n−)  (III)wherein n is at least 2 and m is at least 1, and (b) one cation, whereinthe catalyst is essentially neutrally charged, and further, wherein themolar ratio of phosphorus to the cation is between about 0.5 and about4.0. In another embodiment, the molar ratio of phosphorus to the cationis between about t/2 and about t, wherein t is the charge of the cation.

The catalyst can include an inert support that is constructed of amaterial comprising silicates, aluminates, carbons, metal oxides, andmixtures thereof. Alternatively, the carrier is inert relative to thereaction mixture expected to contact the catalyst. In the context of thereactions expressly described herein, in one embodiment the carrier is alow surface area silica or zirconia. When present, the carrierrepresents an amount of about 5 wt % to about 98 wt %, based on thetotal weight of the catalyst. Generally, a catalyst that includes aninert support can be made by one of two exemplary methods: impregnationor co-precipitation. In the impregnation method, a suspension of thesolid inert support is treated with a solution of a pre-catalyst, andthe resulting material is then activated under conditions that willconvert the pre-catalyst to a more active state. In the co-precipitationmethod, a homogenous solution of the catalyst ingredients isprecipitated by the addition of additional ingredients.

In another embodiment, the catalyst can be sulfate salts; phosphatesalts; mixtures of sulfate and phosphate salts; bases; zeolites ormodified zeolites; metal oxides or modified metal oxides; supercriticalwater, or mixtures thereof.

IV Catalyst Preparation Methods

In one embodiment, the method of preparing the catalyst includes mixingand heating at least two different phosphorus containing compounds,wherein each said compound is described by one of the formulae (IV) to(XXV), or any of the hydrated forms of said formulae:M^(I) _(y)(H_(3−y)PO₄)  (IV)M^(II) _(y)(H_(3−y)PO₄)₂   (V)M^(III) _(y)(H_(3−y)PO₄)₃   (VI)M^(IV) _(y)(H_(3−y)PO₄)₄   (VII)(NH₄)_(y)(H_(3−y)PO₄)  (VIII)M^(II) _(a)(OH)_(b)(PO₄)_(c)   (IX)M^(III) _(d)(OH)_(e)(PO₄)_(f)   (X)M^(II)M^(I)PO₄   (XI)M^(III)M^(I) ₃(PO₄)₂   (XII)M^(IV) ₂M^(I)(PO₄)₃   (XIII)M^(I) _(z)H_(4−z)P₂O₇   (XIV)M^(II) _(v)H_((4−2v))P₂O₇   (XV)M^(IV)P₂O₇   (XVI)(Nn₄)_(z)H_(4″z)P₂O₇   (XVII)M^(III)M^(I)P₂O₇   (XVIII)M^(I)H_(w)(PO₃)_((1+w))  (XIX)M^(II)H_(w)(PO₃)_((2+w))  (XX)M^(III)H_(w)(PO₃)_((3+w))  (XXI)M^(IV)H_(w)(PO₃)_((4+w))  (XXII)M^(II) _(g)M^(I) _(h)(PO₃)_(i)  (XXIII)M^(III) _(j)M_(I) _(k)(PO₃)₁  (XXIV)P₂O₅   (XXV)wherein M^(I) is a monovalent cation; wherein M^(II) is a divalentcation; wherein M^(III) is a trivalent cation; wherein M^(IV) is atetravalent cation; wherein y is 0, 1, 2, or 3; wherein z is 0, 1, 2, 3,or 4; wherein v is 0, 1, or 2; wherein w is 0 or any positive integer;and wherein a, b, c, d, e, f, g, h, i, j, k, and 1 are any positiveintegers, such that the equations: 2a=b+3c, 3d=e+3f, i=2g+h, and 1=3j +kare satisfied.

In one embodiment, the catalyst is prepared by mixing and heating one ormore phosphorus containing compounds of formula (IV), wherein y is equalto 1, and one or more phosphorus containing compounds of formula (V),wherein y is equal to 2. In another embodiment, the catalyst is preparedby mixing and heating M^(I)H₂PO₄ and M^(II)HPO₄. In one embodiment,M^(I) is K⁺ and M^(II) is Ca²⁺, i.e., the catalyst is prepared by mixingand heating KH₂PO₄ and CaHPO₄; or M^(I) is K and M^(II) is Ba²⁺, i.e.,the catalyst is prepared by mixing and heating KH₂PO₄ and BaHPO₄.

In one embodiment, the catalyst is prepared by mixing and heating one ormore phosphorus containing compound of formula (IV), wherein y is equalto 1, one or more phosphorus containing compounds of formula (XV),wherein v is equal to 2. In another embodiment, the catalyst is preparedby mixing and heating M^(I)H₂PO₄ and M^(II) ₂P₂O₇. In one embodiment,M^(I) is K⁺ and M^(II) is Ca²⁺, i.e., the catalyst is prepared by mixingand heating KH₂PO₄ and Ca₂P₂O₇; or M^(I) is K⁺ and M^(II) is Ba²⁺, i.e.,the catalyst is prepared by mixing and heating KH₂PO₄ and Ba₂P₂O₇.

In another embodiment, the molar ratio of phosphorus to the cations inthe catalyst is between about 0.7 and about 1.7; in yet anotherembodiment, the molar ratio of phosphorus to the cations in the catalystis between about 0.8 and about 1.3; and in another embodiment, the molarratio of phosphorus to the cations in the catalyst is about 1.

In another embodiment, the method of preparing the catalyst includesmixing and heating (a) at least one phosphorus containing compound,wherein each said compound is described by one of the formulae (IV) to(XXV), or any of the hydrated forms of said formulae:M^(I) _(y)(H_(3−y)PO₄)  (IV)M^(II) _(y)(H_(3−y)PO₄)₂   (V)M^(III) _(y)(H_(3−y)PO₄)₃   (VI)M^(IV) _(y)(H_(3−y)PO₄)₄   (VII)(NH₄)_(y)(H_(3−y)PO₄)  (VIII)M^(II) _(a)(OH)_(b)(PO₄)_(c)   (IX)M^(III) _(d)(OH)_(e)(PO₄)_(f)   (X)M^(II)M^(I)PO₄   (XI)M^(III)M^(I) ₃(PO₄)₂   (XII)M^(IV) ₂M^(I)(PO₄)₃   (XIII)M^(I) _(z)H_(4−z)P₂O₇   (XIV)M^(II) _(v)H_((4−2v))P₂O₇   (XV)M^(IV)P₂O₇   (XVI)(Nn₄)_(z)H_(4−z)P₂O₇   (XVII)M^(III)M^(I)P₂O₇   (XVIII)M^(I)H_(w)(PO₃)_((1+w))  (XIX)M^(II)H_(w)(PO₃)_((2+w))  (XX)M^(III)H_(w)(PO₃)_((3+w))  (XXI)M^(IV)H_(w)(PO₃)_((4+w))  (XXII)M^(II) _(g)M^(I) _(h)(PO₃)_(i)  (XXIII)M^(III) _(j)M_(I) _(k)(PO₃)₁  (XXIV)P₂O₅   (XXV)wherein y is 0, 1, 2, or 3; wherein z is 0, 1, 2, 3, or 4; wherein v is0, 1, or 2; wherein w is 0 or any positive integer; and wherein a, b, c,d, e, f, g, h, i, j, k, and 1 are any positive integers, such that theequations: 2a=b+3c, 3d=e+3f, i=2g+h, and 1=3j+k are satisfied, and (b)at least one non-phosphorus containing compound selected from the groupconsisting of nitrate salts, carbonate salts, acetate salts, metaloxides, chloride salts, sulfate salts, and metal hydroxides, whereineach said compound is described by one of the formulae (XXVI) to (XL),or any of the hydrated forms of said formulae:M^(I)NO₃   (XXVI)M^(II)(NO₃)₂  (XXVII)M^(III)(NO₃)₃   (XXVIII)M^(I) ₂CO₃   (XXIX)M^(II)CO₃  (XXX)M^(III) ₂(CO₃)₃   (XXXI)(CH₃COO)M^(I)   (XXXII)(CH₃COO)₂M^(II)   (XXXIII)(CH₃COO)³M^(III)   (XXXIV)(CH₃COO)₄M^(IV)   (XXXV)M^(I) ₂O   (XXXVI)M^(II)O  (XXXVII)M^(III) ₂O₃  (XXXVIII)M^(IV)O₂  (XXXIX)M^(I)Cl  (XXXX)M^(II)Cl₂   (XXXXI)M^(III)Cl₃  (XXXXII)M^(IV)Cl₄  (XXXXIII)M^(I) ₂SO₄   (XXXXIV)M_(II)SO₄   (XXXXV)M^(III) ₂(SO₄)₃   (XXXXVI)M^(IV)(SO₄)₂   (XXXXVII)M^(I)OH   (XXXVIII)M^(II)(OH)₂   (XXXIX)M^(III)(OH)₃  (XL).

In another embodiment, the non-phosphorus containing compounds can beselected from the group consisting of carboxylic acid-derived salts,halide salts, metal acetylacetonates, and metal alkoxides.

In one embodiment of the present invention, the molar ratio ofphosphorus to the cations in the catalyst is between about 0.7 and about1.7; in another embodiment, the molar ratio of phosphorus to the cationsin the catalyst is between about 0.8 and about 1.3; and in yet anotherembodiment, the molar ratio of phosphorus to the cations in the catalystis about 1.

In another embodiment of the present invention, the catalyst is preparedby mixing and heating one or more phosphorus containing compounds offormulae (IV) to (XXV) or their hydrated forms, and one or more nitratesalts of formulae (XXVI) to (XXVIII) or their hydrated forms. In anotherembodiment of the present invention, the catalyst is prepared by mixingand heating one or more phosphorus containing compounds of formula (IV)and one or more nitrate salts of formula (XXVII). In a furtherembodiment of the present invention, the catalyst is prepared by mixingand heating a phosphorus containing compound of formula (IV) wherein yis equal to 2, a phosphorus containing compound of formula (IV) whereiny is equal to 0 (i.e., phosphoric acid), and a nitrate salt of formula(XXVII). In yet another embodiment of the present invention, thecatalyst is prepared by mixing and heating K₂HPO₄, H₃PO₄, and Ba(NO₃)₂.In yet another embodiment, the catalyst is prepared by mixing andheating K₂HPO₄, H₃PO₄, and Ca(NO₃)₂.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds offormula (IV) and one or more nitrate salts of formula (XXVIII). In afurther embodiment of the present invention, the catalyst is prepared bymixing and heating a phosphorus containing compound of formula (IV)wherein y is equal to 2, a phosphorus containing compound of formula(IV) wherein y is equal to 0 (i.e., phosphoric acid), and a nitrate saltof formula (XXVIII). In yet another embodiment of the present invention,the catalyst is prepared by mixing and heating K₂HPO₄, H₃PO₄, andMn(NO₃)₂.4H₂O.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds offormula (V) and one or more nitrate salts of formula (XXVI). In anotherembodiment of the present invention, the catalyst is prepared by mixingand heating a phosphorus containing compound of formula (V) wherein y isequal to 2, a phosphorus containing compound of formula (V) wherein y isequal to 0 (i.e., phosphoric acid), and a nitrate salt of formula(XXVI). In yet another embodiment of the present invention, the catalystis prepared by mixing and heating BaHPO₄, H₃PO₄, and KNO₃. In anotherembodiment, the catalyst is prepared by mixing and heating CaHPO₄,H₃PO₄, and KNO₃.

In one embodiment of this invention, the catalyst is prepared by mixingand heating one or more phosphorus containing compounds of formula (V),one or more phosphorus containing compounds of formula (XV), and one ormore nitrate salts of formula (XXVI). In a further embodiment of thisinvention, the catalyst is prepared by mixing and heating a phosphoruscontaining compound of formula (V), wherein y is equal to 0 (i.e.,phosphoric acid); a phosphorus containing compound of formula (XV),wherein v is equal to 2; and a nitrate salt of formula (XXVI). Inanother embodiment of the present invention, the catalyst is prepared bymixing and heating H₃PO₄, Ca₂P₂O₇, and KNO₃. In yet another embodiment,the catalyst is prepared by mixing and heating H₃PO₄, B a₂P₂O₇, andKNO₃.

In another embodiment of this invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds offormula (VI) and one or more nitrate salts of formula (XXVI). In anotherembodiment of this invention, the catalyst is prepared by mixing andheating a phosphorus containing compound of formula (VI), wherein y isequal to 3; a phosphorus containing compound of formula (VI), wherein yis equal to 0 (i.e., phosphoric acid); and a nitrate salt of formula(XXVI). In yet another embodiment of this invention, the catalyst isprepared by mixing and heating MnPO₄.qH₂O, H₃PO₄, and KNO₃.

In one embodiment of this invention, the catalyst is prepared by mixingand heating one or more phosphorus containing compounds of formula (IV),one or more phosphorus containing compounds of formula (IX), and one ormore nitrate salts of formula (XXVII). In another embodiment of thisinvention, the catalyst is prepared by mixing and heating a phosphoruscontaining compound of formula (IV), wherein y is equal to 2; aphosphorus containing compound of formula (IV), wherein y is equal to 0(i.e., phosphoric acid); a phosphorus containing compound of formula(IX), wherein a is equal to 2, b is equal to 1, and c is equal to 1; anda nitrate salt of formula (XXVII). In yet another embodiment of thisinvention, the catalyst is prepared by mixing and heating K₂HPO₄, H₃PO₄,Cu₂(OH)PO₄, and Ba(NO₃)₂.

In one embodiment of this invention, the catalyst is prepared by mixingand heating one or more phosphorus containing compounds of formula (V),one or more phosphorus containing compounds of formula (IX), and one ormore nitrate salts of formula (XXVI). In another embodiment of thisinvention, the catalyst is prepared by mixing and heating a phosphoruscontaining compound of formula (V), wherein y is equal to 3; aphosphorus containing compound of formula (V), wherein y is equal to 0(i.e., phosphoric acid); a phosphorus containing compound of formula(IX), wherein a is equal to 2, b is equal to 1, and c is equal to 1; anda nitrate salt of formula (XXVI). In yet another embodiment, thecatalyst is prepared by mixing and heating Ba₃(PO₄)₂, H₃PO₄, Cu₂(OH)PO₄,and KNO₃.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds describedby one of the formulae (IV) to (XXV) or any of the hydrated forms, andone or more carbonate salts described by one of the formulae (XXIX) to(XXXI) or any of the hydrated forms.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds describedby one of the formulae (IV) to (XXV) or any of the hydrated forms, andone or more acetate salts described by one of the formulae (XXXII) to(XXXV), any other organic acid-derived salts, or any of the hydratedforms.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds describedby one of the formulae (IV) to (XXV) or any of the hydrated forms, andone or more metal oxides described by one of the formulae (XXXVI) to(XXXIX) or any of the hydrated forms.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds describedby one of the formulae (IV) to (XXV) or any of the hydrated forms, andone or more chloride salts described by one of the formulae (XXXX) to(XXXXIII), any other halide salts, or any of the hydrated forms.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds describedby one of the formulae (IV) to (XXV) or any of the hydrated forms, andone or more sulfate salts described by one of the formulae (XXXXIV) to(XXXXVII) or any of the hydrated forms.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds describedby one of the formulae (IV) to (XXV) or any of the hydrated forms, andone or more hydroxides described by one of the formulae (XXXXVIII) to(XL) or any of the hydrated forms.

In one embodiment of the present invention, the catalyst is prepared bymixing and heating one or more phosphorus containing compounds offormulae (IV) to (XXV), and two or more non-phosphorus containingcompounds of formulae (XXVI) to (XL) or their hydrated forms.

In one embodiment, the molar ratio of phosphorus to the cations (i.e.,M^(I)+M^(II)+M^(III)+ . . . ) is between about 0.7 and about 1.7; inanother embodiment, the molar ratio of phosphorus to the cations (i.e.,M^(I)+M^(II)+M^(III)+ . . . ) is between about 0.8 and about 1.3, and inyet another embodiment, the molar ratio of phosphorus to the cations(i.e., M^(I)+M^(II)+M^(III)+ . . . ) is about 1. For example, in anembodiment when the catalyst includes potassium (K⁺) and barium (Ba²⁺),the molar ratio between phosphorus and the metals (K+Ba) is betweenabout 0.7 and about 1.7; and in another embodiment, the molar ratiobetween phosphorus and the metals (K+Ba) is about 1.

When the catalyst includes only two different cations, the molar ratiobetween cations is, in one embodiment, between about 1:50 and about50:1; and in another embodiment, the molar ratio between cations isbetween about 1:4 and about 4:1. For example, when the catalyst includespotassium (K⁺) and barium (Ba²⁺), the molar ratio between them (K:Ba),in one embodiment, is between about 1:4 and about 4:1. Also, when thecatalyst is prepared by mixing and heating K₂HPO₄, Ba(NO₃)₂, and H₃PO₄,the potassium and barium are present, in another embodiment, in a molarratio, K:Ba, between about 2:3 to about 1:1.

In one embodiment, the catalyst can include an inert support that isconstructed of a material comprising silicates, aluminates, carbons,metal oxides, and mixtures thereof. Alternatively, the carrier is inertrelative to the reaction mixture expected to contact the catalyst. Inanother embodiment, the method of preparing the catalyst can furtherinclude mixing an inert support with the catalyst before, during, orafter the mixing and heating of the phosphorus containing compounds,wherein the inert support includes silicates, aluminates, carbons, metaloxides, and mixtures thereof. In yet another embodiment, the method ofpreparing the catalyst can further include mixing an inert support withthe catalyst before, during, or after the mixing and heating of thephosphorus containing compounds and the non-phosphorus containingcompounds, wherein the inert support includes silicates, aluminates,carbons, metal oxides, and mixtures thereof.

Mixing of the phosphorus containing compounds or the phosphoruscontaining and non-phosphorus containing compounds of the catalyst canbe performed by any method known to those skilled in the art, such as,by way of example and not limitation: solid mixing and co-precipitation.In the solid mixing method, the various components are physically mixedtogether with optional grinding using any method known to those skilledin the art, such as, by way of example and not limitation, shear,extensional, kneading, extrusion, and others. In the co-precipitationmethod, an aqueous solution or suspension of the various components,including one or more of the phosphate compounds, is prepared, followedby optional filtration and heating to remove solvents and volatilematerials (e.g., water, nitric acid, carbon dioxide, ammonia, or aceticacid). The heating is typically done using any method known to thoseskilled in the art, such as, by way of example and not limitation,convection, conduction, radiation, microwave heating, and others.

In one embodiment of the invention, the catalyst is calcined.Calcination is a process that allows chemical reaction and/or thermaldecomposition and/or phase transition and/or removal of volatilematerials. The calcination process is carried out with any equipmentknown to those skilled in the art, such as, by way of example and notlimitation, furnaces or reactors of various designs, including shaftfurnaces, rotary kilns, hearth furnaces, and fluidized bed reactors. Thecalcination temperature is, in one embodiment, about 200° C. to about1200° C.; in another embodiment, the calcination temperature is about250° C. to about 900° C.; and in yet another embodiment, the calcinationtemperature is about 300° C. to 600° C. The calcination time is, in oneembodiment, about one hour to about seventy-two hours.

While many methods and machines are known to those skilled in the artfor fractionating particles into discreet sizes and determining particlesize distribution, sieving is one of the easiest, least expensive, andcommon ways. An alternative way to determine the size distribution ofparticles is with light scattering. Following calcination, the catalystis, in one embodiment, ground and sieved to provide a more uniformproduct. The particle size distribution of the catalyst particlesincludes a particle span that, in one embodiment, is less than about 3;in another embodiment, the particle size distribution of the catalystparticles includes a particle span that is less than about 2; and in yetanother embodiment, the particle size distribution of the catalystparticles includes a particle span that is less than about 1.5. Inanother embodiment of the invention, the catalyst is sieved to a medianparticle size of about 50 μm to about 500 μm. In another embodiment ofthe invention, the catalyst is sieved to a median particle size of about100 μm to about 200 μm.

In another embodiment, the catalyst is prepared by the following steps,which comprise: (a) combining a phosphorus containing compound, anitrate salt, phosphoric acid, and water to form a wet mixture, whereinthe molar ratio between phosphorus and the cations in both saidphosphorus containing compound and said nitrate salt is about 1, (b)calcining said wet mixture stepwise at about 50° C., about 80° C., about120° C., and about 450° C. to about 550° C. to produce a dried solid,and (c) grinding and sieving said dried solid to about 100 μm to about200 μm, to produce said catalyst.

In another embodiment, the catalyst is prepared by the following steps,which comprise: (a) combining MnPO₄.qH₂O, KNO₃, and H₃PO₄, in a molarratio of about 0.3:1:1, on an anhydrous basis, and water to give a wetmixture, (b) calcining said wet mixture stepwise at about 50° C., about80° C., about 120° C., and about 450° C. to about 550° C. to give adried solid, and (c) grinding and sieving said dried solid to about 100μm to about 200 μm, to produce said catalyst.

In another embodiment, the catalyst is prepared by the following steps,which comprise: (a) combining Ca₂P₂O₇, KNO₃, and H₃PO₄, in a molar ratioof about 1.6:1:1, and water to give a wet mixture, (b) calcining saidwet mixture stepwise at about 50° C., about 80° C., about 120° C., andabout 450° C. to about 550° C. to give a dried solid, and (c) grindingand sieving said dried solid to about 100 μm to about 200 μm, to producesaid catalyst.

In another embodiment, the catalyst is prepared by the following steps,which comprise: (a) combining a phosphorus containing compound, anitrate salt, phosphoric acid, and water to give a wet mixture, whereinthe molar ratio between phosphorus and the cations in both thephosphorus containing compound and nitrate salt is about 1, (b) heatingsaid wet mixture to about 80° C. with stirring until near dryness toform a wet solid, (c) calcining said wet solid stepwise at about 50° C.,about 80° C., about 120° C., and about 450° C. to about 550° C. to givea dried solid, and (d) grinding and sieving said dried solid to about100 μm to about 200 μm, to produce said catalyst.

In another embodiment, the catalyst is prepared by the following steps,which comprise: (a) combining Ba(NO₃)₂, K₂HPO₄, and H₃PO₄, in a molarratio of about 3:1:4, and water to give a wet mixture, (b) heating saidwet mixture to about 80° C. with stirring until near dryness to form awet solid, (c) calcining said wet solid stepwise at about 50° C., about80° C., about 120° C., and about 450° C. to about 550° C. to give adried solid, and (d) grinding and sieving said dried solid to about 100μm to about 200 μm, to produce said catalyst.

In another embodiment, the catalyst is prepared by the following steps,which comprise: (a) combining Mn(NO₃)₂.4H₂O, K₂HPO₄, and H₃PO₄, in amolar ratio of about 1:1.5:2, and water to give a wet mixture, (b)heating said wet mixture to about 80° C. with stirring until neardryness to form a wet solid, (c) calcining said wet solid stepwise atabout 50° C., about 80° C., about 120° C., and about 450° C. to about550° C. to give a dried solid, and (d) grinding and sieving said driedsolid to about 100 μm to about 200 μm, to produce said catalyst.

In another embodiment, the catalyst is prepared by the following steps,which comprise: (a) combining Ca₂P₂O₇ and KH₂PO₄ in a molar ratio ofabout 3:1 to give a solid mixture, and (b) calcining said solid mixturestepwise at about 50° C., about 80° C., about 120° C., and about 450° C.to about 550° C., to produce said catalyst.

Following calcination and optional grinding and sieving, the catalystcan be utilized to catalyze several chemical reactions. Non-limitingexamples of reactions are: dehydration of hydroxypropionic acid toacrylic acid (as described in further detail below), dehydration ofglycerin to acrolein, dehydration of aliphatic alcohols to alkenes orolefins, dehydrogenation of aliphatic alcohols to ethers, otherdehydrogenations, hydrolyses, alkylations, dealkylations, oxidations,disproportionations, esterifications, cyclizations, isomerizations,condensations, aromatizations, polymerizations, and other reactions thatmay be apparent to those having ordinary skill in the art.

V Examples

The following examples are provided to illustrate the invention, but arenot intended to limit the scope thereof.

Example 1

Solid dibasic potassium phosphate, K₂HPO₄ (36.40 g, 209 mmol, ≧98%;Sigma-Aldrich Co., St. Louis, Mo.; catalog # P3786) was mixed quicklywith an aqueous solution of barium nitrate, Ba(NO₃)₂ (2050 mL of a 0.08g/mL stock solution, 627 mmol, 99.999%; Sigma-Aldrich Co., St. Louis,Mo.; catalog # 202754) at room temperature. Phosphoric acid, H₃PO₄ (58.7mL of an 85 wt %, density=1.684 g/mL, 857 mmol; Acros Organics, Geel,Belgium; catalog # 295700010), was added to the slurry, providing asolution containing potassium (K⁺, M^(I)) and barium (Ba²⁺, M^(II))cations. The final pH of the suspension was about 1.6. Theacid-containing suspension was then dried slowly in a glass beaker at80° C. using a heating plate while magnetically stirring the suspensionuntil the liquid was evaporated and the material was almost completelydried. Heating was continued in a oven with air circulation (G1530A,HP6890 GC; Agilent Corp., Santa Clara, Calif.) at 50° C. for 5.3 h, thenat 80° C. for 10 h (0.5° C./min ramp), following by cooling down at 25°C. The material was calcined at 120° C. for 2 hours (0.5° C./min ramp)followed by 450° C. for 4 hours (2° C./min ramp) using the same oven.After calcination, the material was left inside the oven until it cooleddown by itself at a temperature below 25° C. before it was taken out ofthe oven. Finally, the catalyst was ground and sieved to about 100 μm toabout 200 μm.

Example 2

113.6 g of an 88 wt % L-lactic acid solution (Purac Corp., Lincolnshire,Ill.) was diluted with 386.4 g of distilled water to provide a solutionwith an expected lactic acid concentration of 20 wt %. This solution washeated to 95° C.−100° C. and for 12-30 hours. Then, the solution wascooled to room temperature, and its lactic acid and lactic acidoligomers concentrations were measured by HPLC (Agilent 1100 system;Santa Clara, Calif.) equipped with a DAD detector and a Waters AtlantisT3 column (Catalog # 186003748; Milford, Mass.) using methods generallyknown by those having ordinary skill in the art. The solution wasessentially free of oligomers.

Example 3

454 g of an 88 wt % L-lactic acid solution (Purac Corp., Lincolnshire,Ill.) was diluted with 1,300 g of water. The diluted solution was heatedto 95° C. and held at that temperature with stirring for about 4 to 12hours. Then, the solution was cooled to room temperature, and its lacticacid and lactic acid oligomers concentrations were measured by HPLC(Agilent 1100 system; Santa Clara, Calif.) equipped with a DAD detectorand a Waters Atlantis T3 column (Catalog # 186003748; Milford, Mass.)using methods generally known by those having ordinary skill in the art.The solution was essentially free of oligomers. Finally, the solutionwas further diluted with water to yield a 20 wt % L-lactic acid aqueoussolution and essentially free of oligomers.

Example 4

A 13″ (33 cm) long stainless steel glass lined tube (SGE AnalyticalScience Pty Ltd., Ringwood, Australia) with a 4.0 mm internal diameter(ID) was packed with 3″ (7.6 cm) bed length glass wool and 5″ (12.7 cm)the catalyst from Example 1 (1.6 mL bed volume) to give an 2.55 mL totalpacked bed (8″ or 20.3 cm) and 1.6 mL (5″ or 12.7 cm) of free space atthe top of the reactor. The tube was placed inside an aluminum block andplaced in a clam shell furnace series 3210 (Applied Test Systems,Butler, Pa.), such that the top of the packed bed was aligned with thetop of the aluminum block. The reactor was setup in a down flowarrangement and was equipped with a Knauer Smartline 100 feed pump(Berlin, Germany), a Brooks 0254 gas flow controller (Hatfield, Pa.), aBrooks back pressure regulator, and a catch tank. The clam shell furnacewas heated, such that the reactor wall temperature was kept constant atabout 350° C. during the course of the reaction. The reactor wassupplied with separate liquid and gas feeds that were mixed togetherbefore reaching the catalyst bed. The gas feed was composed of molecularnitrogen at about 360 psig and at a flow of 45 mL/min The liquid feedwas a 20 wt % aqueous solution of L-lactic acid, prepared as in Example2, and fed at 0.045 mL/min (LHSV of 1.7 h⁻¹), giving a residence time ofabout 1 s (GHSV of 3,600 h⁻¹) at STP conditions. After flowing throughthe reactor, the gaseous stream was cooled and the liquid was collectedin the catch tank over 6 h and 42 min (402 min in total) for analysis byoff-line HPLC (Agilent 1100 system; Santa Clara, Calif.) equipped with aDAD detector and a Waters Atlantis T3 column (Catalog # 186003748;Milford, Mass.) using methods generally known by those having ordinaryskill in the art. The gaseous stream was analyzed on-line by GC (Agilent7890 system; Santa Clara, Calif.) equipped with a FID detector andVarian CP-Para Bond Q column (Catalog # CP7351; Santa Clara, Calif.).The acrylic acid aqueous solution had 14.8 wt % acrylic acid and 1.5 wt% lactic acid. The acrylic acid yield was 80%, its selectivity was 85%,and the lactic acid conversion was 94%.

Example 5

The reactor consisted of an electric clam shell furnace (Applied Testsystems, Butler, Pa.) with an 8″ (20.3 cm) heated zone with onetemperature controller connected in series to another electric clamshell furnace (Applied Test Systems, Butler, Pa.) with a 16″ (40.6 cm)heated zone containing two temperature controllers and a reactor tube.The reactor tube consisted of a 13″ (33 cm) borosilicate glass-linedtube (SGE Analytical Science Pty Ltd., Ringwood, Australia)) and a 23″(58.4 cm) borosilicate glass lined tube connected in series using aSwagelok™ tee fitting equipped with an internal thermocouple and havingan inside diameter of 9.5 mm. The head of the column was fitted with a⅛″ (3.2 mm) stainless steel nitrogen feed line and a 1/16″ (1.6 mm)fused silica lined stainless steel liquid feed supply line connected toa HPLC pump (Smartline 100, Knauer, Berlin, Germany) that was connectedto a lactic acid feed tank. The bottom of the reactor was connected to aTeflon-lined catch tank using ⅛″ (3.2 mm) fused silica lined stainlesssteel tubing and Swagelok™ fittings. The reactor column was packed witha plug of glass wool, 13 g of fused quartz, 16″ (40.7 cm) with catalystof Example 1 (47 g and 28.8 mL packed bed volume) and topped with 25 gof fused quartz. The reactor tube was placed in an aluminum block andplaced into the reactor from above in a downward flow. The reactor waspreheated to 375° C. overnight under 0.25 L/min nitrogen. The nitrogenfeed was increased to 0.85 L/min during the experiment. The liquid feedwas a 20 wt % aqueous solution of L-lactic acid, prepared as in Example3, and fed at 0.845 mL/min (LHSV of 1.8 ⁻¹; 50.7 g/h), giving aresidence time of about 1 s (GHSV of 3,600 ⁻¹) at STP conditions. Theclam shell heaters were adjusted to give an internal temperature about350° C. After flowing through the reactor, the gaseous stream was cooledand the liquid was collected in the catch tank for analysis by off-lineHPLC using an Agilent 1100 system (Santa Clara, Calif.) equipped with aDAD detector and a Waters Atlantis T3 column (Catalog # 186003748;Milford, Mass.) using methods generally known by those having ordinaryskill in the art. The gaseous stream was analyzed on-line by GC using anAgilent 7890 system (Santa Clara, Calif.) equipped with a FID detectorand Varian CP-Para Bond Q column (Catalog # CP7351; Santa Clara,Calif.). The crude reaction mixture was cooled and collected over 159 hto give 748 g acrylic acid as a crude mixture in 54% yield, 75% acrylicacid selectivity, and 69% conversion of lactic acid. The acrylic acidyield, corrected for the losses during the evaporating step, was 61% andits selectivity was 89%. The acrylic acid aqueous concentration was 8.4wt %, and that of lactic acid was 6.3 wt %.

Example 6

Experiments without catalyst present further demonstrated the effect offeed stabilization in a quartz reactor. All runs were performed using a0.2 mL reactor. Empty reactors were compared to those packed with fusedsilica (SiO₂) (Sigma-Aldrich Co., St. Louis, Mo.) and Zirblast (SaintGobain Zirpro, Le Pontet Cedex, France) in both stainless steel (SS) andquartz reactors. The results are reported in Table 1 below.

The 0.2 mL reactor system comprised temperature and mass flowcontrollers and was supplied with separate liquid and gas feeds thatwere mixed together before reaching the catalyst bed. The gas feed wascomposed of molecular nitrogen (N₂) and helium (He), which was added asan internal standard for the gas chromatograph (GC) analysis. The liquidfeed was a 20 wt % aqueous solution of L-lactic acid, prepared as in 2,and fed to the top of the reactor while controlling the pump pressure toabout 360 psig to overcome any pressure drop from the catalyst bed.Quartz or stainless steel reactors with an aspect ratio (i.e.,length/diameter) of 75 were used.

Various catalyst beds and gas feed flows were used resulting in a rangeof space velocities (reported herein). The reactor effluent was alsoconnected to another nitrogen dilution line, which diluted the effluentby a factor of two. The helium internal standard normalized anyvariation in this dilution for analytical purposes. The condensedproducts were collected by a liquid sampling system cooled to between6.5° C. to 10° C. while the gaseous products accumulated on the overheadspace of a collection vial. The overhead gaseous products were analyzedusing sampling valves and online gas chromatography (GC).

The feed was equilibrated for 1 hour, after which time the liquid samplewas collected for 2.7 hours and analyzed at the end of the experiment byoffline HPLC. During this time, the gas products were analyzed onlinetwice by GC and reported as an average. Liquid products were analyzed byhigh performance liquid chromatography (HPLC) using an Agilent 1200Series instrument (Agilent Technologies, Santa Clara, Calif.), aSupelcogel-H column (4.6×250 mm; Supelco, St. Louis, Mo.), and adiode-array and a refraction index (RI) detectors. Analytes were elutedisocratically, using 0.005 M H₂SO₄ (aq.) as the elution buffer, over aperiod of 30 min and at a flow of 0.2 mL/min The column and RI detectortemperatures were set at 30° C. Gaseous products were analyzed by anInterscience Compact gas chromatography (GC) system (Interscience BV,Breda, Netherlands) using three detectors (one flame ionizationdetector—FID—and two thermal conductivity—TCD—detectors “A” and “B,”referred to hereinafter as “TCD-A” and “TCD-B,” respectively). Thegaseous products were reported as an average given by two sequential GCchromatograms.

The TCD-A column was an Rt-Q Bond (Restek Corp., Bellefonte, Pa.),having 26 m in length and an I.D. of 0.32 mm with a film thickness of 10um and using a pre-column of 2 m. The pressure was set to 150 kPa, witha split flow of 10 mL/min The column oven temperature was set to 100° C.with a vale oven temperature of 50° C. The flow was set to 5.0 mL/min,with a carrier gas of helium. The TCD-B column was a Mol sieve MSSA(Restek Corp., Bellefonte, Pa.), having a length of 21 m and a filmthickness of 10 μm and using a pre-column of 2 m. The pressure was setto 200 kPa, with a split flow of 10 mL/min The column oven temperaturewas set to 70° C. with a vale oven temperature of 50° C. The flow wasset to 2.0 mL/min, with a carrier gas of argon. The FID column was aRTx-624 (Restek, Bellefonte, Pa.), having a length of 28 m and an innerdiameter of 0.25 mm with a film thickness of 14 mm and using apre-column of 2 m. The pressure was set to 100 kPa, with a split flow to20 mL/min The column oven temperature was set to 45° C. with a vale oventemperature of 50° C.

VI Results

TABLE 1 LA Con- AA AA PA Inert Reactor GHSV, version, Selectivity,Yield, Yield, Packing Material (h⁻¹) (%) (%) (%) (%) Empty Quartz 3,45318 0 0.2 0.2 Empty SS 3,453 71.7 0 0.2 13.7 Fused Quartz 3,489 25 0.051.4 2.9 SiO₂ Fused SS 3,489 68.6 0 0 13.4 SiO₂ Zirblast Quartz 3,48921.8 0 0 0.2 Zirblast SS 3,489 70 0 0 13

The results reported in Table 1 indicate that at high space velocities,very little byproducts were observed when quartz reactors were used,with or without inert packing. Thus, it was determined that the use ofquartz reactors minimized two important side reactions: lactic acidoligomerization and reduction to propionic acid. This is important toevaluating the true activity of catalysts.

The foregoing description is given for clearness of understanding only,and no unnecessary limitations should be understood therefrom, asmodifications within the scope of the invention may be apparent to thosehaving ordinary skill in the art.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A process for converting hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof to acrylic acid,acrylic acid derivatives, or mixtures thereof comprising the followingsteps: a) Providing an aqueous solution comprising hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof, whereinsaid hydroxypropionic acid is in monomeric form in said aqueoussolution; b) Combining said aqueous solution with an inert gas to forman aqueous solution/gas blend; c) Evaporating said aqueous solution/gasblend to produce a gaseous mixture; and d) Dehydrating said gaseousmixture by contacting said gaseous mixture with a dehydration catalystunder a pressure of at least about 80 psig, producing said acrylic acid,acrylic acid derivatives, or mixtures thereof.
 2. The process of claim1, wherein the pressure is from about 80 psig to about 550 psig.
 3. Theprocess of claim 1, wherein the pressure is from about 150 psig to about500 psig.
 4. The process of claim 1, wherein the temperature during theevaporating step is from about 165° C. to about 450° C.
 5. The processof claim 1, wherein the temperature during the evaporating step is fromabout 250° C. to about 375° C.
 6. The process of claim 1, wherein theGHSV in the evaporating step is from about 720 h⁻¹ to about 36,000 h⁻¹.7. The process of claim 1, wherein the temperature during thedehydrating step is from about 150° C. to about 500° C.
 8. The processof claim 1, wherein the temperature during the dehydrating step is fromabout 300° C. to about 450° C.
 9. The process of claim 1, wherein theGHSV in the dehydrating step is from about 720 h⁻¹ to about 36,000 h⁻¹.10. The process of claim 1, wherein the GHSV in the dehydrating step isabout 3,600 h⁻¹.
 11. The process of claim 1, wherein thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof comprise from about 5 wt % to about 50 wt % of said aqueoussolution.
 12. The process of claim 1, wherein the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof comprise fromabout 10 wt % to about 25 wt % of said aqueous solution.
 13. The processof claim 1, wherein the inert gas is selected from the group consistingof air, nitrogen, helium, argon, carbon dioxide, carbon monoxide, steam,and mixtures thereof.
 14. The process of claim 1, wherein the gaseousmixture comprises from about 1 mol % to about 10 mol % of saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof.
 15. The process of claim 1, wherein said evaporating step isperformed in a reactor, wherein said reactor has an interior surfacecomprising material selected from the group consisting of quartz,borosilicate glass, silicon, hastelloy, inconel, manufactured sapphire,stainless steel, and mixtures thereof.
 16. The process of claim 1,wherein said dehydrating step is performed in a reactor, wherein saidreactor has an interior surface comprising material selected from thegroup consisting of quartz, borosilicate glass, silicon, hastelloy,inconel, manufactured sapphire, stainless steel, and mixtures thereof.17. The process of claim 1, wherein said hydroxypropionic acid is lacticacid.
 18. The process of claim 17, wherein the acrylic acid selectivityfrom the lactic acid is at least 50%.
 19. The process of claim 17,wherein the acrylic acid selectivity from the lactic acid is at least80%.
 20. The process of claim 17, wherein the propanoic acid selectivityfrom the lactic acid is less than about 5%.
 21. The process of claim 17,wherein the propanoic acid selectivity from the lactic acid is less thanabout 1%.
 22. The process of claim 17, wherein the conversion of saidlactic acid is more than about 50%.
 23. The process of claim 17, whereinthe conversion of said lactic acid is more than about 80%.
 24. Theprocess of claim 1, wherein said evaporating step is performed under apressure of from about 80 psig to about 550 psig.
 25. A process forconverting hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof to acrylic acid, acrylic acid derivatives, or mixturesthereof comprising the following steps: a) Providing an aqueous solutioncomprising hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof, wherein said hydroxypropionic acid comprises oligomersin said aqueous solution; b) Heating said aqueous solution at atemperature from about 50° C. to about 100° C. to remove said oligomersof said hydroxypropionic acid and produce an aqueous solution ofmonomeric hydroxypropionic acid; c) Combining said aqueous solution ofmonomeric hydroxypropionic acid with an inert gas to form an aqueoussolution/gas blend; d) Evaporating said aqueous solution/gas blend toproduce a gaseous mixture; and e) Dehydrating said gaseous mixture bycontacting said mixture with a dehydration catalyst, producing saidacrylic acid, acrylic acid derivatives and mixtures thereof.
 26. Theprocess of claim 25, wherein, after said heating step, said oligomerscomprise less than about 5 wt % based on the total amount ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof.
 27. A process for converting hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof to acrylic acid,acrylic acid derivatives, or mixtures thereof comprising the followingsteps: a) Providing an aqueous solution comprising hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof, whereinsaid hydroxypropionic acid is in monomeric form in said aqueoussolution; b) Combining said aqueous solution with an inert gas to forman aqueous solution/gas blend; c) Evaporating said aqueous solution/gasblend to produce a gaseous mixture; d) Dehydrating said gaseous mixtureby contacting said mixture with a dehydration catalyst, producing saidacrylic acid, acrylic acid derivatives, or mixtures thereof; and e)Cooling said acrylic acid, acrylic acid derivatives, or mixtures thereofat a GHSV of more than about 360 h⁻¹.
 28. The process of claim 27,wherein the GHSV in the cooling step is more than about 720 h⁻¹.
 29. Aprocess for converting lactic acid to acrylic acid comprising thefollowing steps: a) Diluting an about 88% lactic acid aqueous solutionwith water to form an about 20 wt % lactic acid aqueous solution; b)Heating said about 20 wt % lactic acid aqueous solution at a temperaturefrom about 95° C. to about 100° C. to remove oligomers of said lacticacid, producing a monomeric lactic acid aqueous solution comprising atleast 95 wt % of said lactic acid in monomeric form based on the totalamount of lactic acid; c) Combining said monomeric lactic acid aqueoussolution with nitrogen to form an aqueous solution/gas blend; d)Evaporating said aqueous solution/gas blend in a reactor with insidesurface of borosilicate glass at a GHSV of about 7,200 h⁻¹ at atemperature from about 300° C. to about 350° C. to produce a gaseousmixture comprising about 2.5 mol % lactic acid and about 50 mol % water;e) Dehydrating said gaseous mixture in a reactor with inside surface ofborosilicate glass at a GHSV of about 3,600 h⁻¹ at a temperature fromabout 350° C. to about 425° C. by contacting said mixture with adehydration catalyst under a pressure of about 360 psig, producing saidacrylic acid; and f) Cooling said acrylic acid to give an acrylic acidsolution at a GHSV from about 360 h⁻¹ to about 36,000 h⁻¹.
 30. A processfor converting hydroxypropionic acid, derivatives of hydroxypropionicacid, and mixtures thereof to acrylic acid, acrylic acid derivatives, ormixtures thereof comprising the following steps: a) Providing an aqueoussolution comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof, wherein said hydroxypropionic acid isin monomeric form in said aqueous solution, and wherein thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof comprise from about 10 wt % to about 25 wt % of said aqueoussolution; b) Combining said aqueous solution with an inert gas to forman aqueous solution/gas blend; c) Evaporating said aqueous solution/gasblend to produce a gaseous mixture; and d) Dehydrating said gaseousmixture by contacting said mixture with a dehydration catalyst producingsaid acrylic acid, acrylic acid derivatives, or mixtures thereof. 31.The process of claim 30, wherein the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof comprise about 20wt % of said aqueous solution.
 32. A process for converting alkyllactates to acrylic acid, acrylic acid derivatives, or mixtures thereofcomprising the following steps: a) Providing alkyl lactates or asolution comprising alkyl lactates and a solvent; b) Combining saidalkyl lactates or said solution comprising said alkyl lactates and saidsolvent with an inert gas to form a liquid/gas blend; c) Evaporatingsaid liquid/gas blend to produce a gaseous mixture; and d) Dehydratingsaid gaseous mixture by contacting said gaseous mixture with adehydration catalyst under a pressure of at least about 80 psig,producing said acrylic acid, acrylic acid derivatives, or mixturesthereof.
 33. The process of claim 32, wherein said alkyl lactates areselected from the group consisting of methyl lactate, ethyl lactate,butyl lactate, 2-ethylhexyl lactate, and mixtures thereof.
 34. Theprocess of claim 32, wherein the solvent is selected from the groupconsisting of water, methanol, ethanol, butanol, 2-ethylhexanol,isobutanol, isooctyl alcohol, and mixtures thereof.